Optical systems typically include many components, which interact to generate, transmit, modify, and detect light. These components often are modular, permitting them to be combined in different ways for different applications. This modularity enhances flexibility but may diminish efficiency. In particular, gaps between modular components may permit stray (e.g., room) light to enter the optical system, lowering the signal-to-background ratio. Such gaps also may permit signal light to exit the system, lowering the signal.
Stray light has been reduced mostly by reducing the amount of ambient light available to enter the system. In some cases, stray light has been reduced by placing the entire optical system in a light-fight room, which is darkened when the optical system is in use. Unfortunately, this approach has a variety of shortcomings. It requires a dedicated room, which wastes space. It also requires the operator of the optical system to work in the dark, which is inherently unsafe, because the operator may have difficulty seeing the equipment, and because the operator may become drowsy. In other cases, stray light has been reduced by placing all or part of the optical system in a light-tight container. Unfortunately, this approach also has a variety of shortcomings. It hinders access to the components. It also reduces flexibility, because components must be chosen and arranged to fit within the container.
Signal light has been retained mostly by precisely aligning the optical system. Unfortunately, this approach also has a variety of shortcomings. In particular, it works best when optical components are fixed in position. It works less well when optical components are subject to vibration or when optical components must be moved during operation, such as in switching among plural light sources, detectors, and optical paths.